Light detection and ranging or “LIDAR” refers to a technique for measuring distances to visible surfaces by emitting light and measuring properties of the reflections of the light. A LIDAR system has a light emitter and a light sensor. The light emitter may comprise a laser that directs light into an environment. When the emitted light is incident on a surface, a portion of the light is reflected and received by the light sensor, which converts light intensity to a corresponding electrical signal.
A LIDAR system has signal processing components that analyze reflected light signals to determine the distances to surfaces from which the emitted laser light has been reflected. For example, the system may measure the propagation time of a light signal as it travels from the laser emitter, to the surface, and back to the light sensor. A distance is then calculated based on the flight time and the known speed of light.
Distortions of the reflected light signal caused by a variety of factors may cause traditional LIDAR systems to inaccurately determine a time at which the reflected light returns to the light sensor. For example, a one nanosecond variation in the return signal time may correspond to a change in the estimated distance of roughly 15 centimeters. Some of the factors that can cause distortions of the reflected light signal may include highly reflective surfaces, surfaces that are very close to the LIDAR unit, etc.
Since thousands, or even millions, of measurements may be made every second by a LIDAR system, it is not easy to detect the existence of such small variations in return signal time of reflected light signals. In many cases, discovering this problem is made more difficult by the fact that the variations in return time of reflected light signals simply go undetected. The LIDAR system detects the delayed return and inaccurately gauges the distance to the object.
Moreover, in some high-noise or low-noise conditions, discriminating a return signal from noise may be difficult. For example, sunny conditions may create a strong noise power band that can obscure the return signal. Conventional LIDAR systems set a threshold and filter out any signals below the threshold. This effectively filters out the noise, but also filters out weaker returns falling under the threshold. Additionally, since the strength of return signals is lower for more distant objects, setting a high threshold effectively reduces the range of the LIDAR system.